A basic commercial process for recovery of hydrogen sulfide from acid gas streams is the Claus process. The basic chemical reactions occurring in the Claus process are presented in Equations (I), (II), and (III). EQU H.sub.2 S+1/2O.sub.2 .revreaction.H.sub.2 O+S (I) EQU H.sub.2 S+3/2O.sub.2 .revreaction.H.sub.2 O+SO.sub.2 (II) EQU H.sub.2 S.revreaction.H.sub.2 +S (III) EQU 2H.sub.2 S+SO.sub.2 .revreaction.2H.sub.2 O+3S (IV)
Reactions (I), (II), and (III) occur in a thermal zone (reaction furnace) sometimes called a muffle furnace, and reaction (IV) occurs primarily in a catalytic zone (catalytic reactor). The Claus process thus comprises two stages: (1) a thermal stage above, for example, 1850.degree. F., and typically in the range of 2000.degree. F. to 3000.degree. F., and (2) a catalytic stage generally, for example, between a temperature somewhat above the sulfur dewpoint of the gas stream and about 700.degree. F.
In the thermal zone, a gas stream containing hydrogen sulfide can be burned with an oxidant in a reaction furnace to form hot combustion gases containing a substantial amount of free sulfur which can be condensed after cooling the hot combustion gases. This condensation can take place in a first waste heat boiler and subsequently in a sulfur condenser. Thereafter, the lean gas goes to the catalytic reactor system wherein the reaction of Equation (IV) takes place.
Typically, the oxidant is air. However, other oxidants which are suitable include pure oxygen, oxygen enriched air, and sulfur dioxide. The tail gas from this system was, at one time, released to the atmosphere or, more usually, passed to an incinerator. As environmental control requirements have become more strict, work has been done to improve tail gas clean-up. Some of these newer processes reduce all sulfur species to hydrogen sulfide by reduction before further processing. Although it is known that the normal Claus tail gas contains some hydrogen and carbon monoxide produced in the thermal reaction zone, there is a possibility that there will be incomplete hydrogenation at some times in plant operation. For this reason, the practice has been to include a reducing gas generator in these designs. This represents an initial investment plus operating costs.
The system of the present invention eliminates the need for a separate hydrogen generator as a result of a modification of the Claus furnace.
An object of this invention is to provide an improved Claus thermal reaction zone.
A further object of this invention is to provide a method for the operation of the Claus system which eliminates the need for a separate hydrogen generator in the tail gas treating system.
Other objects and advantages of the present invention will be apparent to those skilled in the art upon reading the present disclosure.